The present invention relates to an ink jet recording apparatus having an ink jet recording head for ejecting ink droplets in accordance with the print data and forming the dots on the recording medium.
Generally, an ink jet recording head (hereinafter referred to as a “recording head”) comprises a plurality of nozzle orifices, a pressure generating chamber in communication with each nozzle orifice, and a piezoelectric vibrator for varying the pressure of the pressure generating chamber. And the recording head ejects the ink of the pressure generating chamber as ink droplets through nozzle orifices owing to a pressure change within the pressure generating chamber caused by vibrating the piezoelectric vibrator in accordance with a print signal.
In the recording apparatus employing the above recording head, the recording head is mounted on a carriage capable of reciprocating in a main scanning direction, and ejects ink droplets onto the recording sheet while reciprocating in a widthwise direction of the recording sheet, thereby printing an image or character through use of a dot matrix onto the recording sheet
In nozzle orifices ejecting ink droplets successively during the printing operation, since new ink are successively supplied thereto, clogging is hardly occurred. However, in the nozzle orifices located at the upper end or lower end to eject ink droplets less frequently, the ink is dried and become viscous near the nozzle orifices while printing, possibly causing the clogging. From the time when the recording head is reciprocated once to make the printing to the time when the print data corresponding to one reciprocation is input, the recording head is enabled to stand by at the stand-by position, but the drying of the ink progresses while the stand-by, giving rise to an ejection failure such as flight curvature because the viscous ink resides near the nozzle orifices.
To deal with such a problem, a “flushing” for expelling the viscous ink near the nozzle orifices to prevent an occurrence of print failure is performed by applying a drive signal irrespective of the print data to the piezoelectric vibrator at a start timing of printing after the print data is entered in the stand-by state, as one of the preliminary operations for starting the printing.
However, in the related ink jet recording apparatus, since the flushing operation is performed successively, a part of the viscous ink near the nozzle orifices is expelled by flushing to make a clear portion, and the ink is successively ejected through the clear portion, so that the viscous ink residing around the clear portion is difficult to expel effectively. In this state, a meniscus 41 is intruded deeply and obliquely to avoid a viscous ink lump 45, and is not recovered sufficiently, making the behavior of the meniscus 41 extremely unstable and causing a flight curvature on subsequent ejecting, it being apprehended that the stable ejection characteristics can not be obtained, as shown in FIG. 9. If the meniscus 41 is intruded deeply and obliquely, it is also apprehended that a bubble is entered into the nozzle orifice 40 to prevent ejecting of ink droplets. In this figure, pressure generating chamber 43 is in communication with a nozzle orifice 40. A vibration plate 44 makes up a part of the pressure generating chamber 43. A piezoelectric vibrator 42 is provided for vibrating the vibration plate 44.